U.S. patent number 6,656,394 [Application Number 09/785,088] was granted by the patent office on 2003-12-02 for method and apparatus for high throughput generation of fibers by charge injection.
This patent grant is currently assigned to Charge Injection Technologies, Inc.. Invention is credited to Arnold J. Kelly.
United States Patent |
6,656,394 |
Kelly |
December 2, 2003 |
Method and apparatus for high throughput generation of fibers by
charge injection
Abstract
A fiber is formed by providing a stream of a solidifiable fluid,
injecting the stream with a net charge so as to disrupt the stream
and allowing the stream to solidify to form fibers.
Inventors: |
Kelly; Arnold J. (Princeton
Junction, NJ) |
Assignee: |
Charge Injection Technologies,
Inc. (Monmouth Junction, NJ)
|
Family
ID: |
22672837 |
Appl.
No.: |
09/785,088 |
Filed: |
February 16, 2001 |
Current U.S.
Class: |
264/10 |
Current CPC
Class: |
B05B
5/10 (20130101); D01D 5/0023 (20130101); D01D
5/0069 (20130101); D01D 5/0092 (20130101); D01D
5/08 (20130101); B05B 5/001 (20130101); Y10T
428/2904 (20150115) |
Current International
Class: |
B05B
5/08 (20060101); B05B 5/10 (20060101); D01D
5/08 (20060101); B29B 009/00 () |
Field of
Search: |
;264/10 ;425/6,174.6
;428/359,401 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1527592 |
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Oct 1978 |
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GB |
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WO 98/03267 |
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Jan 1998 |
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WO |
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WO 99/18893 |
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Apr 1999 |
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WO |
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WO 00/22207 |
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Apr 2000 |
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WO |
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WO 00/67694 |
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Nov 2000 |
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WO |
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WO 01/26610 |
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Apr 2001 |
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WO |
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WO 01/27365 |
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Apr 2001 |
|
WO |
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Other References
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"Green" Polymers, May 5-7, 1997, pp. 141-150. .
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Produced by Electrospinning, Polymer Engineering and Science, vol.
39, No. 5, May 1999, pp. 849-854. .
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of Nanofibers, Structure Formation in Polymeric Fibers, Chapter 6,
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Abstract of Japan 03220305A (Sep. 27, 1991). .
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Properties of Some Nanofibers, Textile Research Journal, 71(4),
323-328 (2001). .
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657-665. .
Phillip Gibson, Heidi Schreuder-Gibson and Christopher Pentheny,
Electrospinning Technology: Direct Application Of Tailorable
Ultrathin Membranes, Journal Of Coated Fabrics, vol. 28--Jul. 1998,
pp. 63-73. .
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Oct. 2001, pp. 50-53. .
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and Applications, eSpin Technologies, Inc., date unknown. .
Michel M. Bergshoef and G. Julius Vansco, Transparent
Nanocomposites With Ultrathin Electrospun Nylon-4,6 Fiber
Reinforcement, Advanced Materials, 1999, 11, No. 16, pp. 1362-1365.
.
Bill Smith, U.S. Army Develops Fabric Membrane To Provide
Multipurpose Protection, Technical Textiles Int'l, p. 6, May
1998,.
|
Primary Examiner: Tentoni; Leo B.
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz
& Mentlik, LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims benefit of U.S. Provisional Application
Ser. No. 60/183,450, filed Feb. 18, 2000, the disclosure of which
is hereby incorporated by reference herein.
Claims
I claim:
1. A method of producing fibers, comprising: a) providing a stream
of a solidifiable fluid; b) providing the stream with a net charge
so as to disrupt the stream by passing the stream through a body
defining an orifice so that the stream passes through an electric
field before exiting the orifice; and c) allowing the disrupted
stream to solidify to form fibers.
2. The method of claim 1, wherein the step of providing the stream
with a net charge includes injecting a net charge into the
stream.
3. The method of claim 2, wherein the step of injecting a net
charge includes injecting a net charge so as to develop a self
electric field for the stream of at least 0.5 megavolts per
meter.
4. The method of claim 1, wherein the solidifiable fluid comprises
a liquid polymer.
5. The method of claim 4, wherein the liquid polymer comprises a
molten polymer.
6. The method of claim 1, wherein the solidifiable fluid is
selected from the group consisting of: a liquid glass; a liquid
polyester; liquid polytetrafluoroethylene; liquid polyethylene
terephthalate; liquid polybutylene terephthalate; and liquid
thermoplastic polyurethane.
7. The method of claim 1, wherein the solidifiable fluid comprises
a liquid solution including a polymeric material.
8. The method of claim 5, wherein the step of providing a stream
includes heating a polymeric material and the step of allowing the
stream to solidify comprises allowing the disrupted stream to
cool.
9. The method of claim 7, wherein the step of providing a stream
includes providing a polymeric material in a solvent and the step
of allowing the stream to solidify comprises allowing the solvent
to evaporate.
10. The method of claim 1, wherein the step of providing a stream
of a solidifiable fluid comprises passing the solidifiable fluid
through an orifice at a rate of at least 0.1 grams per second.
11. The method of claim 10, wherein the step of providing a stream
of a solidifiable fluid comprises passing the solidifiable fluid
through an orifice at a rate of at least 0.5 grams per second.
12. The method of claim 11, wherein the step of providing a stream
of a solidifiable fluid comprises passing the solidifiable fluid
through an orifice at a rate of at least 1 gram per second.
13. The method of claim 1, wherein the step of providing the stream
with a net charge comprises passing the stream between a pair of
electrodes in the vicinity of the orifice while maintaining a
potential difference between the electrodes.
14. The method of claim 13, wherein one of the pair of electrodes
comprises the body defining the orifice.
15. The method of claim 1, wherein the step of injecting a net
charge comprises passing the stream past an electron gun located
adjacent the orifice.
16. The method of claim 1, further comprising heating the disrupted
stream as it passes out of the orifice.
17. The method of claim 1, wherein the step of providing the stream
with a net charge provides the stream with a charge density of at
least 0.5 coulombs per cubic meter.
18. A method of producing fibers, comprising: a) providing a
plurality of streams of solidifiable fluid; b) providing the
plurality of streams with a net charge so as to disrupt the streams
by passing each stream through a structure defining an orifice so
that the stream passes through an electric field prior to exiting
the orifice; and c) allowing each disrupted stream to solidify to
form fibers.
19. A method of forming a charged solid, comprising: a) providing a
stream of a solidifiable fluid; b) providing the stream with a net
charge by passing the stream through a body defining an orifice so
that the stream passes through an electric field prior to exiting
the orifice; c) allowing the stream of solidifiable fluid to
solidify while still charged.
20. The method of claim 19, wherein the stream disrupts under the
influence of the net charge.
21. The method of claim 19, wherein the stream of solidifiable
fluid has a maximum charge mobility of 10.sup.-6 m.sup.2
/V.sup..cndot. sec.
22. The method of claim 19, wherein the stream of solidifiable
fluid has a minimum net charge of 0.1 coulombs per cubic meter.
23. A method of forming fibers comprising the steps of: (a)
providing a stream of a solidifiable fluid at a rate of at least
about 0.01 grams per second; (b) injecting electrical charge into
the stream of solidifiable fluid, whereby the stream will tend to
disperse and form filaments; and (c) solidifying the filaments.
24. The method of claim 23 wherein the step of injecting electrical
charge is performed so as to inject at least about 0.6 coulomb per
cubic meter of said solidifiable fluid.
25. The method of claim 23 wherein the step of providing a stream
comprises providing a stream at a rate of at least 0.1 grams per
second.
26. The method of claim 25 wherein the step of providing a stream
comprises providing a stream at a rate of at least 1 gram per
second.
27. A method of forming fibers comprising the steps of: (a)
providing a stream of a solidifiable fluid at a rate of at least
about 0.01 grams per second; (b) injecting at least about 0.6
coulomb of electrical charge per cubic meter of fluid into said
stream of solidifiable fluid, whereby the stream will tend to
disperse and form filaments; and (c) solidifying the filaments.
28. A method of forming fibers comprising the steps of a) providing
a stream of a solidifiable fluid at a rate of at least about 0.03
millimeters per second; b) injecting electrical charge into said
stream of solidifiable fluid, whereby the stream will tend to
disperse and form filaments; and c) solidifying the filaments.
29. A method as claimed in claim 28, wherein the step of injecting
electrical charge is performed so as to inject at least 1 coulomb
per cubic meter of said solidifiable fluid.
30. The method of claim 28, wherein the step of providing a stream
comprises providing a stream at a rate of at least 0.1 millimeters
per second.
31. The method of claim 30, wherein the step of providing a stream
comprises providing a stream at a rate of at least about 0.5
milliliters per second.
Description
FIELD OF THE INVENTION
The present invention relates to electrostatic methods and
apparatus for forming fibers from fluids.
BACKGROUND OF THE INVENTION
In conventional commercial production of low diameter fibers, a
liquid material such as a liquid polymer is forced through a small
orifice in an apparatus referred to as a spinneret. The liquid
polymers utilized in many fibers are extremely viscous and
difficult to pass through a small orifice. These methods encounter
practical difficulties.
Certain methods of electrostatic formation of fibers from liquid
polymers are known. These methods use an electrode defining an
orifice. The liquid is passed through the orifice, from a first
side of the electrode to a second side. An oppositely charged
surface is remotely disposed with respect to the electrode, on the
second side of the electrode, to attract and collect the fibers
formed after the fluid issues from the orifice. These methods
require large potential differences developed over the large air
gap between the orifice and the charged surface on which the fibers
are collected. The electric field developed over the air gap is
relied upon to develop the necessary charge within the fluid and
attenuate the fluid. The attenuated fluid then solidifies into
fibers. For low conductivity fluids, such as liquid polymers
utilized to develop fibers for commercial applications such as
fabrics, the flow rates attained by these methods are unacceptable.
Known methods also include the use of a capillary needle as the
electrode and orifice discussed above. Fibers having diameters of
50 nanometers and up have been produced utilizing these
methods.
Electrostatic formation of fibers has great potential and it has
been known that electrostatic formation of fibers would present a
much more convenient and efficient method of producing fibers.
However, despite considerable effort to develop these methods,
these methods have been unable to handle commercially acceptable
flow rates.
SUMMARY OF THE INVENTION
The present invention addresses these needs.
In accordance with one aspect of the present invention, a method of
producing fibers comprises providing a stream of a solidifiable
fluid, providing the stream with a net charge so as to disrupt the
stream by passing the stream through a body defining an orifice so
that the stream passes through an electric field before exiting the
orifice, and allowing the disrupted stream to solidify to form
fibers. "Solidify" as used herein, means a marked change in
viscosity or change in state such that the material tends to retain
a definite shape. "Solidify" as used herein includes a change in
the fluid to an elastomeric fiber, rigid or semi-rigid fibers, and
solid or semi-solid fibers.
Preferably, the step of providing the stream with a net charge
includes injecting a net charge into the stream. The step of
injecting a net charge preferably includes injecting a net charge
so as to develop a self electric field for the stream of at least
0.5 megavolts per meter. Charge injection of the solidifiable fluid
achieves a high charge density in the fluid. Charge injection
creates a strong "self-field" within and in proximity to the fluid
stream, and the fluid stream forms fibers under the influence of
the self-field.
In certain preferred embodiments, a pair of electrodes is provided
in the vicinity of the orifice while a potential difference is
maintained between the electrodes. One of the pair of electrodes
may comprise the body. An electric field is developed between the
electrode and the body so that the stream is provided with a net
charge. Charge injection occurs within the stream of fluid, in the
space between the electrode and the body defining the orifice.
The self-field within and immediately surrounding the fluid stream
causes the fluid stream to break into highly elongated filaments
which solidify to form solid fibers. A further surface remote from
the orifice such as a container or a collection reel may be used to
collect the fibers. This surface may be at the same potential as
the body defining the orifice, or may be at a different potential.
However, there is no need to provide a large potential difference
between this surface and the body. Typically, both the body
defining the orifice and the collecting surface are grounded.
The limit on the flow rate of the solidifiable fluid is the size of
the orifice so that throughput orders of magnitude greater than the
known electrostatic methods is achieved. The improved throughput is
surprising. Embodiments in accordance with the invention have
achieved throughputs great enough for industrial production of
fibers.
The method, in certain preferred embodiments, comprises heating the
disrupted stream as it passes out of the orifice. The step of
providing the stream with a net charge preferably provides the
stream with a charge density of at least 0.5 coulombs per cubic
meter.
The step of injecting a net charge, in certain preferred
embodiments, comprises passing the stream past an electron gun
located adjacent the orifice.
The step of providing a stream of a solidifiable fluid may comprise
passing the solidifiable fluid through an orifice at a rate of at
least 0.1 grams per second, in certain embodiments, or a rate of at
least 0.5 grams per second, in other embodiments. The solidifiable
fluid may be passed through an orifice at a rate of at least 1 gram
per second.
The step of providing a stream of solidifiable fluid may include
heating a polymeric material and the step of allowing the stream to
solidify may comprise allowing the disrupted stream to cool. The
step of providing a stream of a solidifiable fluid may comprise
providing a polymeric material in a solvent and the step of
allowing the stream to solidify may comprise allowing the solvent
to evaporate.
The solidifiable fluid may comprise a liquid polymer, for example.
In certain preferred embodiments, the liquid polymer comprises a
molten polymer.
The solidifiable fluid may comprise a liquid glass, a liquid
polyester, such as polytetrafluoroethylene, polyethylene
terephthalate ("PET"), polybutylene terephthalate, or a liquid
thermoplastic polyurethane.
The solidifiable fluid may comprise a liquid solution including a
polymeric material, such as LEXAN.RTM. and methylene chloride, or
tetrahydrofurane and urethane.
Another aspect of the present invention, is an electrostatically
formed fiber produced by the providing a stream of a solidifiable
fluid, providing the stream with a net charge so as to disrupt the
stream by passing the stream through a body defining an orifice so
that the stream passes through an electric field prior to exiting
the orifice, and allowing the disrupted stream to solidify to form
fibers. The fiber may be formed of a polyester, a polytetra
fluoroethylene, polyethylene terephthalate, polybutylene
terephthalate, thermoplastic polyurethane, carbon, or glass. The
fibers preferably have a diameter of less than 100 micrometers,
more preferably less than 10 micrometers. In certain preferred
embodiments, the fiber has a diameter of less than 500 nanometers,
preferably less than 100 nanometers, even more preferably less than
20 nanometers.
In another aspect of the present invention, a method of producing
fibers comprises providing a plurality of streams of solidifiable
fluid. Each of the plurality of streams is provided with a net
charge so as to disrupt the streams by passing each stream through
a structure defining an orifice so that the stream passes through
an electric field prior to exiting the orifice. Each disrupted
stream is allowed to solidify to form fibers. Orifices for multiple
streams may be utilized in an assembly for generating fibers on a
large scale.
In another aspect of the present invention, a method of forming a
charged solid comprises providing a stream of a solidifiable fluid,
providing the stream with a net charge by passing the stream
through a body defining an orifice so that the stream passes
through an electric field prior to exiting the orifice, and
allowing the stream of solidifiable fluid to solidify while still
charged. In certain preferred embodiments, the stream disrupts
under the influence of the net charge. Preferably, the stream of
solidifiable fluid has a maximum charge mobility of 10.sup.-6
m.sup.2 /V.sup..cndot. sec. Preferably, the stream of solidifiable
fluid has a minimum net charge of 0.1 coulombs per cubic meter.
In yet another aspect of the present invention, an apparatus for
producing fibers comprises a feed system adapted to deliver a
stream of molten polymeric material, and a charge injection device
adapted to provide the stream with a net charge so as to disrupt
the stream, said device comprising a body defining an orifice and
being arranged so that the stream passes through an electric field
prior to exiting the orifice.
The feed system preferably comprises at least one heater for
melting the polymeric material. In certain preferred embodiments,
the charge injection device comprises a pair of electrodes, in
which one of the pair of electrodes comprises the body defining the
orifice. In other embodiments, the charge injection device
comprises an electron gun.
In another aspect of the present invention, a method of forming
fibers comprises providing a stream of a solidifiable fluid at a
rate of at least about 0.02 grams per second, injecting electrical
charge into the stream of solidifiable fluid, whereby the stream
will tend to disperse and form filaments, and solidifying the
filaments. The method preferably comprises injecting electrical
charge so as to inject at least about 1 coulomb per cubic meter.
The method preferably comprises providing the stream of fluid at a
rate of at least 0.1 gram per second and more preferably at least 1
gram per second.
In another aspect of the present invention, a method of forming
fibers comprises providing a stream of a solidifiable fluid,
injecting at least about 1 coulomb of electrical charge per cubic
meter of fluid into the stream of solidifiable fluid, whereby the
stream will tend to disperse and form filaments and solidifying the
filaments. Preferably, the stream is provided at a rate of at least
about 0.02 grams per second.
In another aspect of the present invention, a method of forming
fibers comprises providing a stream of a solidifiable fluid at a
rate of at least about 0.03 milliliters per second, injecting
electrical charge into the stream of solidifiable fluid, whereby
the stream will tend to disperse and form filaments, and
solidifying the filaments. The method preferably comprises
injecting electrical charge so as to inject at least about 1
coulomb per cubic meter into the solidifiable fluid. The method
preferably comprises providing the stream of fluid at a rate of at
least 0.1 gram per second and more preferably at least 1 gram per
second.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects and advantages of the present
invention will become better understood with regard to the
following description, appended claims and accompanied drawing
where:
FIG. 1 is a schematic cross-sectional view of an apparatus for
performing a method in accordance with an embodiment of the present
invention;
FIG. 2 is a schematic view of a fluid feed system for the
embodiment of FIG. 1;
FIG. 3 is a view of a stream of fluid disrupted under the influence
of a net charge;
FIG. 4 is a cross-sectional view of an apparatus for implementing a
method in accordance with another embodiment of the present
invention;
FIG. 5 is a schematic circuit diagram of a controller for the
apparatus of FIG. 4;
FIG. 6 is a schematic front-right partial perspective view of the
apparatus of FIGS. 4 and 5;
FIG. 7 is a schematic partial cross-sectional view of an apparatus
for implementing the method in accordance with a further embodiment
of the present invention;
FIG. 8 is a front-left partial perspective view of the apparatus of
FIG. 7;
FIG. 9 is a partial front elevational view of the apparatus of
FIGS. 7 and 8;
FIG. 10 is a side elevational view, partially in cross-section, of
an apparatus in accordance with another embodiment of present
invention;
FIG. 11 is a cross-sectional view taken along line 11--11 in FIG.
10;
FIG. 12 is a side-elevational view, partially in section, of an
apparatus in accordance with a further embodiment of the present
invention;
FIG. 13 is a cross-sectional view taken along line 13--13 in FIG.
12;
FIG. 14 is a graph illustrating the electrode to body current vs.
operating voltage of the apparatus of FIG. 1.
DETAILED DESCRIPTION
An apparatus for performing a method in accordance with an
embodiment of the invention comprises a dispersing apparatus 10, as
shown in FIG. 1. An electrically conductive metallic body 11 with a
central axis 14 has a liquid supply line 19 formed therein and
opens into a central chamber 12. The body 11 shown in FIG. 1 has a
generally cylindrical shape. A shape including as few corners as
possible is preferred. However, the shape of the body 11 is not
essential. The body 11 defines a first end 13 and a second end 15
opposite from first end 13 for the apparatus 10. The body 11
defines a forward wall 16 at the first end 13 of the apparatus. The
forward wall 16 has an orifice 22 opening therethrough on central
axis 14. An electrically insulating support 38 is disposed within
the central chamber 12 of the body 11. Insulator 38 is generally
cylindrical and coaxial with the body 11. The insulator defines a
plurality of liquid distribution channels 44 extending generally
radially and a set of axially extensive grooves 49 adjacent the
outer periphery of the insulator. Radial channels 44 merge with one
another adjacent the central axis 14 and merge with the grooves 49.
Further, the radial channels 44 and axial grooves 49 communicate
with the supply line 19 of body 11, so that the supply line is in
communication, via the radial channels 44, with all the axial
grooves 49 around the periphery of insulator 38. A fluid source 37
delivers a fluid to supply line 19 so that the fluid flows through
channels 44 and grooves 49 to the chamber 12. Insulator 38 may be
formed of any substantially rigid dielectric material, such as a
glass, non-glass ceramic, thermoplastic polymer or thermosetting
polymer.
A charge injection device 21 comprises a central electrode 25. A
central electrode 25 is mounted within insulator 38 and
electrically insulated from the body 11 by insulator 38. Central
electrode 25 has a pointed forward end 42 having a tip 40 disposed
in alignment with orifice 22 and in close proximity thereto.
Preferably, the forward tip 40 of central electrode 25 is formed
from a setaceous element having numerous small points 43. For
example, the setaceous element may be formed from ytrria stabilized
zirconia-tungsten eutectic. Alternatively, the electrode may
comprise a metal rod. A ground electrode 52 is mounted remote from
body 11 and remote from orifice 22. Although electrode 52 is
schematically illustrated as a flat plate in FIG. 1, its
geometrical form is not critical. For example, the ground electrode
52 may comprise a drum. Where the atomized liquid is directed into
a vessel, pipe or other enclosure, the ground electrode 52 may be a
wall of the enclosure.
Ground electrode 52 is at a reference or ground electrical
potential. The body 11 is connected via a resistor to the ground
potential 47. Tip 40 of central electrode 25 is connected to a
voltage potential source 50. The foregoing components of the
dispersing apparatus may be generally similar to the corresponding
components of the apparatus called the SPRAY TRIODE.RTM. atomizer,
disclosed in certain embodiments of U.S. Pat. No. 4,255,777, the
disclosure of which is hereby incorporated by reference herein.
The solidifiable fluid may comprise any solidifiable polymer in a
liquid form, such as a liquid polymer or a liquid solution
including a polymeric material. In certain preferred embodiments,
the fluid comprises a molten polymer such as polyethylene
terephthalate ("PET"). The molten PET is supplied from fluid source
37, which may comprise a feed system, such as the feed system 37
shown in FIG. 2. The feed system of FIG. 2 is a laboratory
apparatus. For commercial applications, a commercially available
extruder for melting the PET and supplying the same under pressure
is used. For example, a screw type extruder, which melts polymeric
material at least in part under the influence of friction within
the extruder, may be used. These extruders are well known in the
art.
The feed system 37 includes a reservoir 41 in which PET in a
granular form is placed. The reservoir has a first end 45 and a
second end 46 opposite from the first end 45. The dispersing
apparatus 10 is attached to the reservoir 41 at the first end 45
through a coupling 48. Preferably, a plurality of heaters 51 is
used to melt the granular PET. As shown in FIG. 2, a band heater
51a is located at the coupling 48 between the reservoir 41 and
dispersing apparatus 10. Heaters are also preferably located on the
dispersing apparatus 10. A band heater 51b is located on the
apparatus 10, at the first end 13 of the apparatus 10. A band
heater 51c is also located on the dispersing apparatus 10, at the
second end 15 of the apparatus 10.
The reservoir 41 is preferably heated interiorly and exteriorly.
The reservoir 41 includes a rope heater 51d located closer to the
second end 46 than band heaters 51e, which are located closer to
the first end 45 of the reservoir 41. A heater is also preferably
disposed within the reservoir, such as rod heater 51f, which is
mounted on the second end 46 by a thermocouple 54.
The heaters heat the granulated PET contained in the reservoir 41
to the operating temperature for melting the PET. The temperature
for melting the PET is between about 290.degree. C. and 295.degree.
C.
For example, the particular feed system 37 shown in FIG. 2 has a
maximum operating temperature of 310.degree. C. The reservoir 41
shown in FIG. 2 is a 1 liter reservoir. The heaters, by way of
example, may be: a 150 Watt band heater for band heater 51a; a 100
Watt band heater for band heater 51b; a 100 Watt band heater for
band heater 51c; a 500 Watt rope heater for rope heater 51d; 650
Watt band heaters for band heaters 51e; and a 600 Watt rod heater
for rod heater 51f. A sufficient amount of heat must be generated
to melt enough PET for operation. For example, heaters 51a-f
generate enough heat to melt several hundred grams of PET. The
reservoir must have sufficient capacity for storing the molten PET.
Preferably, the temperature is monitored at several points manually
or, more preferably, automatically monitored. For example, the
temperature may be monitored at points Ta, Tb, Td, Ti, To, Tm, Tr,
Tt, and Tu shown in FIG. 2 to ensure that the temperature at those
points does not exceed the maximum temperature for the components
of the system.
The feed system 37 includes an assembly 60 for supplying pressure
to the reservoir 41. The assembly 60 is attached to thermocouple 54
and supplies a pressurized gas, such as air to the reservoir 41.
The pressure supplied to the reservoir provides a flow of molten
PET through the apparatus 10. The assembly 60 has a first end 58
attached to a supply of pressurized gas and a second end 56 which
leads to a vacuum or vent. The actual pressure required to supply a
flow of molten PET depends upon the viscosity of the particular PET
material utilized.
In embodiments using molten polymer, apparatus 10 is preferably
designed to accommodate the heat of the molten polymer. By way of
example, the atomizer disclosed in certain embodiments of U.S. Pat.
No. 4,255,777, the disclosure of which is hereby incorporated by
reference herein, may be mounted in a stainless steel 1/2" tee,
modified to accommodate the atomizer. Such a device withstands
pressures over 40 bar while being exposed to temperatures of
325.degree. C. and up.
In operation, the molten PET is supplied through supply line 19 of
the apparatus 10, flowing through the radial channels 44 and axial
grooves 49 within the body 11. The PET flows to chamber 12 through
the grooves 49 on either side of the electrode 25. As the PET flows
towards orifice 22 in a stream, the PET flows past the tip 40 of
the electrode 25. The voltage source 50 is operated to develop a
charge on the tip 40 of the electrode 25. An electric field is
developed between the electrode 25 and the body 11. The PET flows
through the electric field between the electrode 25 and body 11
prior to exiting through the orifice 22. As the PET flows through
the electric field, a charge is injected into the PET stream,
providing the stream with a net charge.
Various portions of the stream of charged fluid repel each other
under the influence of the net charge. The stream is disrupted
under the influence of the net charge and begins to disperse, as
shown in FIG. 3. At the same time, the molten PET cools and begins
to solidify. Although the invention is not limited to any theory of
operation, it is believed that the stream 62 issuing from the
orifice 22 in a longitudinal direction 64 begins to disperse into
elongated filaments 66 extending outwardly from the stream 62.
Filaments 66 are developed at intervals along the stream 62. It is
believed that these elongated filaments 66 of PET solidify into
fibers as the molten PET cools. The fibers collect in the space
outside the orifice 22 and may be directed toward electrode 52, in
circumstances where the fibers retain a charge.
A throughput orders of magnitude greater than the known
electrostatic methods discussed above is achieved for liquid
polymers. By utilizing orifices having different sizes and varying
the pressure of the solidifiable fluid, the throughput flow rate
can be increased. The improved throughput is surprising in that
prior art electrostatic methods of generating fibers have been
unsuccessful in producing fibers on a large scale. Utilizing the
above-disclosed method, fibers of PET have been produced at flow
rates on the order of 1 gram per second through a single
orifice.
Embodiments in accordance with the invention have achieved
throughputs great enough for industrial production of fibers for
use in non-woven materials, fabrics, filtration materials,
agricultural applications and materials used in medical fields.
The solidifiable fluid may comprise virtually any solidifiable
fluid with a conductivity and/or charge mobility low enough that
the charge injection process does not short out. In other words, if
the charge travels though the fluid to the body of the apparatus
prior to exiting the orifice of the apparatus, the stream of fluid
will not receive a net charge and will not disrupt into filaments
66 (see FIG. 3) under the influence of net charge. If the fluid
conductivity exceeds a conductivity on the order of 10.sup.4 cu
and/or charge mobility exceeds 10.sup.-6 m.sup.2 /V.sup..cndot.
sec, the fluid is inappropriate for using with the apparatus 10.
When textile grade standard IV 0.640 molten PET was utilized in a
device as shown in FIGS. 1 and 2, the current from the electrode to
the body of the device, plotted against the input voltage is as
shown in FIG. 14.
Fibers may be formed from any solidifiable material. For example, a
ceramic and binder material may be used to form fibers in methods
according to embodiments of the present invention. Metals, for
example, may also be used to form fibers in other methods according
to embodiments of the present invention. Another example is forming
fibers from liquid flowing glass. Solidifiable fluids for forming
fibers in methods according to the present invention include molten
polymers and polymeric materials in a liquid solution. For example,
the following solutions may be used: Tetra Hydrofurane and Urethane
and LEXAN.RTM. and methylene chloride. Methods in accordance with
embodiments of the invention may be used to form rigid or
semi-rigid fibers. Fibers may be formed by solidifying the stream
of solidifiable liquid into fibers of a solid or semi-solid
material.
Fibers may be formed from any polymeric material. Just by way of
example, fibers may be formed from polyesters, including: the
polytetra fluoroethylene material known as TEFLON.RTM.;
polyethylene terephthalate (PET); polybutylene terephthalate;
polycarbonates such as LEXAN.RTM.; thermoplastic polyurethanes such
as the materials known as PELLETHANE.RTM. or ESTANE.RTM., Nylon,
and a number of others. By manipulating the properties of the
liquid polymer, or selection of the type of liquid polymer, fibers
can be produced having virtually any strength and can be used as
reinforcement of materials.
Direct charge injection for producing fibers may be achieved
utilizing the charge injection devices described in certain
embodiments of U.S. Pat. Nos. 4,255,777, 4,991,774, 5,093,602,
5,378,957, 5,391,958, and 5,478,266, the disclosures of which are
hereby incorporated by reference herein. Certain preferred
embodiments of the present invention include charge injection
devices having features disclosed in certain embodiments of U.S.
Pat. Nos. 6,161,785, 6,206,307, 6,227,465 and 6,474,573, the
disclosures of which are all hereby incorporated by reference
herein.
In electrostatic atomizers, corona induced breakdown in the
vicinity of the exiting charged stream has been experienced. When a
critical level of charge is reached, corona-induced breakdown
occurs and the plume of atomized fluid collapses. Should it be
necessary or desirable to reduce the occurrence of this phenomenon
in the dispersing apparatus, the dispersing apparatus 110 may be
provided with a control-feedback system as shown in FIGS. 4-6 and
as disclosed in certain embodiments of U.S. patent application Ser.
No. 09/430,633, filed Oct. 29, 1999, the disclosure of which is
hereby incorporated by reference herein. Alternatively, the pulsing
atomizer of certain embodiments of U.S. patent application Ser. No.
09/430,632, filed Oct. 29, 1999, the disclosure of which is hereby
incorporated by reference herein, may be used to address corona
induced breakdown.
The embodiment of the invention shown in FIGS. 4-6 has a dispersing
apparatus 110 with a body 111 defining an orifice 122. A voltage
potential source 150 is connected to a central electrode 125 and a
fluid source 137 supplies a fluid to the passages within the body
111. These elements are substantially as discussed above in
connection with FIGS. 1 and 2 and similar elements in FIGS. 1 and 4
have similar reference numerals.
The dispersing apparatus 110 includes a sensor comprising a loop
antenna 170. The antenna, for example, may be comprised of a
0.5-millimeter diameter insulated wire in the shape of an open loop
curving around the orifice 122 of the apparatus 110. Power source
150 comprises a high voltage power source including a controller
180 and DC--DC converter 162 shown in FIG. 5. The controller 180
comprises a circuit having a central processing unit ("CPU") 163
connected to a dual digital resistor 164. Resistor 164 is connected
to an analog switch 181, which is in turn connected to an amplifier
182. Amplifier 182 is connected to the DC--DC converter. A
transistor 185 is connected to the switch 181 and CPU 163. The
circuit includes another amplifier 183, to which the antenna 170 is
connected. Amplifiers 182 and 183 may be included in one component,
in other embodiments. There are many components known to those of
ordinary skill in the art that can be utilized in the circuit shown
in FIG. 5. The controller 180 is operated to vary the operating
voltage for the dispersing apparatus 110, supplied by the voltage
source 150. The antenna 170 detects signals and the components of
the controller 180 control the operating voltage of the voltage
source 150 to avoid corona-induced breakdown as disclosed in U.S.
Pat. No. 6,206,307.
The orifice may, in certain preferred embodiments, be provided with
a fixture 200 for varying the size of the orifice. As shown in FIG.
7, an apparatus 210, which is generally similar to the apparatus 10
as shown in FIGS. 1 and 2, includes the fixture 200 mounted on
first end 213. Fixture 200 comprises a generally cylindrical sleeve
220 having a wall 221 which partially covers forward wall 216 of
the apparatus 210. The wall 221 has a curvilinear edge 223 which
joins with the sleeve 220. Wall 221 ends in the substantially
linear edge 224 interrupted by a circular cutout 225. The cutout
225 is positioned along the wall 224 so that orifice 222 of the
apparatus 210 may be exposed and unobstructed by the wall 221. The
fixture 200 has an initial position, as shown in FIG. 8, in which
the orifice 222 is exposed in cutout 225. Fixture 200 is rotatably
mounted on the apparatus 210 and rotatable in a direction 226 so as
to move wall 221 over the orifice 222, as shown in FIG. 9. In this
manner, the orifice 222 may be partially obstructed by wall 221,
thereby diminishing the effective size of the orifice 222. If the
size of the orifice 222 should be changed to change the flow rate
of the fluid during operation, the fixture 200 is rotated to vary
the size of the orifice 222. In addition, it may be desirable to
change the size of the orifice between operations of the apparatus
210. For example, the apparatus 210 may be operated with a
solidifiable fluid having a first viscosity. The size of the
orifice may be changed to operate the same apparatus 210 with a
solidifiable fluid having a second viscosity to achieve the same
throughput as achieved for the fluid having the first viscosity. In
another example, the apparatus 210 may be operated with the orifice
222 partially obstructed by wall 221 of the fixture 200. In order
to flush the orifice 222 of any debris or clogs, the fixture 200
may be rotated in a direction opposite to direction 226 to fully
expose the orifice 222 and power to the central electrode may be
turned off so that uncharged fluid issues from orifice 222. In this
manner, the orifice 222 may be flushed of debris. The variable
orifice disclosed in certain embodiments of U.S. Pat. No.
6,161,785, the disclosure of which is hereby incorporated by
reference herein, may also utilized with a dispersing apparatus as
discussed in the embodiments above.
Certain embodiments disclosed in U.S. Pat. No. 6,474,573, the
disclosure of which is hereby incorporated by reference herein,
provide multiple orifices in a single nozzle referred to as the
SPRITZ CHIP device. Similar structures can be used to provide
multiple fluid streams for fibers formation. For example, such an
embodiment is shown in FIGS. 10 and 11. A dispersing apparatus
includes a body 320 having a first wall 324 and a second wall 325
generally parallel to the first wall but spaced therefrom. The
first wall 324 defines a plurality of discharge orifices 326. The
first wall 324 may be formed from a conductive material or from a
dielectric material such as silicon dioxide. Where the first wall
324 comprises a dielectric material, an external electrode 350
common to all the orifices 326 is formed on an exterior surface 328
of the first wall 324 by depositing a coating of an electrically
conductive material such as a metal on this surface. First wall 324
and second wall 325 are held apart from one another by an
insulating internal structure 321, which may comprise a plurality
of walls subdividing the space between the walls into a large
number of hexagonal chambers or internal spaces 322. Hexagonal
spaces 322 are disposed on center with orifices 326, so that each
orifice is aligned with the center of one hexagonal space. Emitter
electrodes 344 are mounted to second wall 325 and are in alignment
with orifices 326. Second wall 325 may be comprised of an
insulative material, or incorporates a dielectric layer 327 and a
conductive layer 323 electrically connected to all of the emitter
electrodes 344. The second wall 325 has a large number of fluid
passages 330 extending through it. These orifices form a filter for
filtering the solidifiable fluid to be utilized in forming fibers.
The relative size of the passages 330 depends upon the particular
solidifiable fluid utilized and the fluid viscosity. The size of
the passages 330 is exaggerated in FIGS. 10 and 11 for quality of
illustration.
Dispersing apparatus according to this embodiment of the invention
can be fabricated using micro-mechanical fabrication techniques,
similar to the techniques used for forming semiconductor chips and
related devices. Photo-etching techniques, plating, vacuum
deposition or other conventional techniques used in semiconductor
fabrication may be used. The emitter electrodes can be formed by
etching and/or deposition on the same mass of material used to form
the second wall 325. For example, tungsten emitters can be formed
by sputtering, by vapor deposition or by chemical vapor deposition.
In a variant of this technique, the internal structure 321 can be
fabricated together with the second wall 325 so that the internal
structure is integral with the second wall. Also, although the
internal structure is shown as completely dividing the space
between walls 324 and wall 325 into entirely separate spaces 322,
these spaces may communicate with one another.
In another embodiment of the invention, the spaces 422 are open to
the passages for delivery of the solidifiable fluid. (See FIGS. 12
and 13). Thus, second wall 425 does not include holes for filtering
the solidifiable fluid. The remaining features of this embodiment
are generally similar to those of FIGS. 10 and 11 and similar
features of FIGS. 12 and 13 have reference numerals similar to
FIGS. 10 and 11.
The devices shown in FIGS. 10 through 13 are used in a manner
similar to the device discussed above with reference to FIGS. 1 and
2. For example, the electrode 344 is connected to a high voltage
terminal of a power supply, whereas the second electrode 350 is
connected to a lower potential, preferably by connecting the second
electrode to ground. A third, grounded electrode (not shown), is
provided remote from the device. The solidifiable fluid is
delivered to the hexagonal space 322 through the fluid entry holes
330 and passes out through discharge orifices 326. Here again, the
electric field between electrode 344 and the external electrode 350
causes injection of electrical charge into the fluid passing
downstream into discharge orifices 326. The injected electrical
charge causes dispersement of the fluid and the formation of
fibers.
The devices shown in FIGS. 10 through 13 can be fabricated in any
size, and the size of the orifices, hexagonal spaces and the
distance between first wall and second wall depend upon the
solidifiable fluid utilized.
The use of multiple orifices in the device provides several
significant advantages. First, plugging or other problems affecting
one orifice will not cause complete failure of the device. Also,
any number of orifices can be used to provide a device with greater
or lesser flow capability without altering the other operating
characteristics of the device. A multi-orifice device can be
utilized to produce fibers on a large, industrial or commercial
scale.
Charged injection to form fibers in accordance with the invention
can also be accomplished using an electron beam in proximity to an
orifice so that electrons in the beam impinge on the fluid, either
as it issues from the orifice, or just before the stream passes
through the orifice. Electron beam devices previously used for
atomization of liquids are disclosed in U.S. Pat. Nos. 5,378,957,
5,093,602, 5,391,958, the disclosures of which are hereby
incorporated by reference herein and copies of which are annexed
hereto.
Although the invention herein has been described with reference to
particular embodiments, it is to be understood that these
embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the invention as
defined by the appended claims.
EXAMPLES
In the following examples, two types of PET were utilized in the
apparatus of FIGS. 1 and 2. The diameter of the orifice was 406
micrometers and standard IV 0.640 PET was fed through the
apparatus. The size of the orifice affects the operating pressure
required for a given throughput of the fluid, as well as the
attainable charged density. Larger orifice diameters reduce the
operating pressure and achieve a lower charge density. In the 406
micrometer diameter apparatus, the maximum charge density achieved
in the stream of PET is about 62% of the maximum charge density
achieved in a 250-micrometer diameter orifice apparatus. The
reservoir of the apparatus was pressurized to 19 bar (275 PSI). The
flow rate of the molten PET through the 406 micrometer diameter
orifice was 0.8 grams per second. The volumetric flow rate of the
PET was about 0.57 milliliters per second.
The charge density of the fluid issuing from the orifice of the
dispersing apparatus varies across the diameter of the orifice. The
outer portions of the stream of fluid are highly charged, as
compared with the central portion of the stream. The mean charge
density for the 406 micrometer apparatus was 0.88
coulombs/m.sup.3.
An operating voltage of only 2.7 kilovolts was required to charge
the molten PET sufficiently to develop fibers. This is a surprising
feature of the fiber development process. When the apparatus is
utilized with Mil-C-7024 type II calibrating fluid, 5-6 kilovolts
is required to disrupt the stream of calibrating fluid.
The fibers generated in the 406 micrometer diameter apparatus were
generally smooth and tapered. A small fraction of fibers were
branched and included junction points between fibers. Many of the
fibers were hollow. It is believed that the hollow fibers resulted
from bubbles trapped in the molten PET extend during the fiber
generation process. Many of the textile grade PET fibers had
diameters of 100 micrometers or more.
The 406 micrometer diameter apparatus was utilized with standard IV
0.589 PET. This PET is less viscous than the textile grade PET
discussed above. The textile grade PET has a viscosity of 1845
poise at 295.degree. C. and the less viscous PET has a viscosity of
1180 poise at 295.degree. C.
The feed system was operated at the same pressure. The fibers
produced had diameters below 100 micrometers and many had diameters
of 10 micrometers or less. Relatively large droplets of about 700
micrometers in diameter were attached to the fibers. It is believed
that the textile grade PET did not produce such droplets because
the textile grade PET cooled before droplets were formed. As seen
in FIG. 3, for example, the stream of fluid issuing from the
orifice disrupts into elongated filaments which may eventually form
droplets. On the other hand, the branching produced in the textile
grade PET indicates that the stream of PET cooled prior to
formation of independent fibers. Thus, controlled heating of the
zone outside the orifice, in which fiber generation occurs, may be
utilized to enhance the production of fibers. The PET fibers
retained a charge after being formed. The finer fibers retained a
higher charge and were attracted the ground electrode spaced from
the orifice.
Methods according to embodiments of the present invention inject a
net charge into the solidifiable fluid and the charge is trapped
within the fiber after the fluid solidifies. The charged fibers can
be later used as, for example, material for an electrostatic
filter.
The PET fibers had diameters of 10 micrometers or less. Much
smaller fibers may be produced utilizing methods and apparatus in
accordance with embodiments of the invention. In another example,
an apparatus as shown in FIGS. 1 and 2 was utilized to form fibers
from a thermoplastic polyurethane known as PELLETHANE.RTM.,
provided in a solution with tetra hydrofurane. The fibers produced
ranged in diameter from about 20 nanometers to about 500
nanometers.
* * * * *